The present invention relates to a cement additive composition or, more particularly, to a cement additive composition capable of improving the dispersibility of the cement particles in a cement-based mixture, i.e. cement paste, mortar or concrete, admixed therewith and capable of improving the workability of a cement-based mixture by increasing the flowability or by preventing decrease in the flowability with a lapse of time.
As is known, cement-based mixtures such as cement paste, mortar and concrete must be formulated with water in an excessive volume over the minimum required for the hardening or setting reaction of the cement because a cement-based mixture prepared with water in just the minimum volume for the hardening reaction has a consistency not suitable for satisfactory working due to the strong cohesive force between the cement particles. The increase of the volume of water in a cement-based mixture, however, is necessarily accompanied by the decrease in the strength of the hardened body of the mixture which can be compensated only by increasing the amount of cement formulated in the mixture but an overly increase in the amount of cement in a unit volume of the cement-based mixture results in increase of the heat evolution by the hardening reaction leading to increased danger of crack formation in the hardened body.
Another serious problem with cement-based mixtures at a working site is the inconsistency of the workability of the cement-based mixtures from time to time. Cement-based mixtures are usually prepared by blending the base materials at a plant and transported to a working site by a concrete mixer car so that the variation in the time taken for the transportation due to the difference in the distance between the mixing plant and the working site or the degree of traffic jam directly influences the consistency and hence workability of the cement-based mixture.
A further difficulty is sometimes encountered in pressurized pumping of a cement-based mixture through a pipe. That is, when resumption of pumping of a cement-based mixture is desired after a certain length of time after an interruption, the mixture held in the pipe has acquired an increased consistency or decreased flowability so that the pumping pressure for resumption must be unduly increased or, in the worst case, the pipe is partly or completely clogged by the hardened mixture.
As is mentioned above, the most simple and convenient method for improving the flowability of a cement-based mixture is to increase the volume of water formulated therein with the resultant unavoidable disadvantages of increased danger of crack formation or failure of the hardened body of the mixture. Accordingly, it is eagerly desired to develop a cement additive resulting in water volume reduction, and capable of improving the dispersibility of the cement particles and also imparting to the cement-based mixture satisfactorily workable flowability along with an increase in the time period of the thus improved flowability.
Various kinds of cement additives having such an effect have been proposed and developed. Some of them include salt-type condensation products of sodium naphthalene sulfonate and formaldehyde and salt-type condensation products of alkylnaphthalene sulfonic acid and formaldehyde. These conventional cement additives are indeed effective in improving the flowability of a cement-based mixture to some extent although the effectiveness thereof is not quite satisfactory and the thus improved flowability of a cement-based mixture admixed therewith cannot be retained for a sufficiently long time as desired.
The inventors have accordingly undertaken extensive investigations to develop a cement additive capable of imparting a cement-based mixture with improved flowability which is maintained over a longer period of time and discovered and proposed previously that a combination of a saponified product of a sulfonated copolymer of styrene and maleic acid with one or more of certain other flowability-improving additives can satisfactorily serve for the above mentioned purpose (see Japanese Patent Kokai No. 6033242 and U.S. Ser. No. 629,316). This proposal, however, is not so effective as to completely solve the problem because the sulfonation of the above mentioned copolymer is performed in a complicated process with a limited yield of the sulfonation product of, usually, about 70% and the proposed cement additive has little contribution to the lasting improvement of the flowability of a cement-based mixture.